Reconstruction of Patterns of Differential Subsidence Using an Episodic Stratigraphic Model

  1. P. A. Allen and
  2. P. Homewood
  1. E. J. Anderson,
  2. Peter W. Goodwin and
  3. Peter T. Goodmann

Published Online: 5 MAY 2009

DOI: 10.1002/9781444303810.ch24

Foreland Basins

Foreland Basins

How to Cite

Anderson, E. J., Goodwin, P. W. and Goodmann, P. T. (1986) Reconstruction of Patterns of Differential Subsidence Using an Episodic Stratigraphic Model, in Foreland Basins (eds P. A. Allen and P. Homewood), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303810.ch24

Author Information

  1. Department of Geology, Temple University, Philadelphia, PA 19122, USA

Publication History

  1. Published Online: 5 MAY 2009
  2. Published Print: 22 DEC 1986

ISBN Information

Print ISBN: 9780632017324

Online ISBN: 9781444303810



  • reconstruction of patterns of differential subsidence using episodic stratigraphic model;
  • thickness variation in PACS;
  • columnar section of Keyser Formation at Tyrone, Pennsylvania;
  • Keyser PACs;
  • application of hypothesis of Punctuated Aggradational Cycles (PACs);
  • subsidence analysis;
  • PAC hypothesis


Applying a general model of episodic stratigraphic accumulation, the Hypothesis of Punctuated Aggradational Cycles (PACs), it is possible to reconstruct patterns of differential subsidence within short time intervals in the Appalachian Foreland Basin. As small-scale (1–5 m thick) time-stratigraphic shallowing-upward cycles, PACs provide the necessary chronologic and palaeoenvironmental control for discriminating the amount of stratigraphic thickness attributable to differential subsidence. Correlation of PACs in the shallow carbonate facies of the Keyser Formation of central Pennsylvania permits precise determination of significant differential subsidence between localities only 60 km apart. Over this distance an 11·5 m difference in stratigraphic thickness (30 m versus 18·5 m) can be attributed to differential subsidence by establishing correlative horizons which were topographically level surfaces at the time of deposition. Correlation is accomplished by dividing the entire section into PACs at each locality, tracing individual PACs between pairs of localities and by correlating three major deepening events, distinguished at all localities by marked facies changes. Two PACs, one at the bottom of the sequence studied and one in the middle of the Keyser Formation aggraded to sea-level and were selected for subsidence analysis. The tops of each of these PACs once represented essentially horizontal synchronous surfaces. Difference in stratigraphic thickness between these surfaces can only be explained by differential subsidence. Differential subsidence (11·5 m in 60 km of distance) was progressively greater toward the south and was introduced into the stratigraphic record non-uniformly (more in some PACs than in others). Only by applying a model of small-scale episodic accumulation is it possible to recognize the synchronous palaeoisotopographic surfaces necessary for interpreting basin dynamics at this scale. In that PACs are predicted to occur in all facies affected by relative sea-level fluctuations, this method has potential for very detailed reconstruction of the patterns and amounts of differential subsidence in the stratigraphic record, especially in nearshore facies.